fix: generate_json_schema.lua removes final newline

Problem:
"generate_json_schema.lua" removes final newline from
"schema/packspec_schema.json".

Solution:
Append a newline before writing.

Author: justinmk

scripts/generate_json_schema.lua

@@ -3,7 +3,7 @@
 -- local cjson = require('cjson')
 local schema = require('packspec.schema')
 local format_json = require('utils.format_cjson')
-local encoded_json = format_json(schema, "\n", "  ")
+local encoded_json = format_json(schema, "\n", "  ")..'\n'
 
 local file = io.open('schema/packspec_schema.json', 'w')